1. Field of Invention
The present invention relates to a semiconductor process. More particularly, the present invention relates to a method for forming a metal silicide layer.
2. Description of Related Art
As the integration of semiconductor device increases, the pattern and the line width in the device gradually decrease. The contact resistance of the gate and the conductive line in the device thereby increases, leading to a higher RC delay and adversely affecting the operating speed. Since the resistance of metal silicide is lower than polysilicon and the thermal stability of metal silicide is higher than a typical inter-metal dielectric material, forming metal silicide on a gate can lower the resistance between the gate and the metal interconnect.
Among the various metal silicide, nickel silicide currently attracts much attention because of its low resistivity. However, during the removal process for removing unreacted metal nickel after the thermal process for transforming a portion of the metal nickel into the nickel silicide is performed, the etchant agent used in the removal process would attack the nickel silicide through the grain boundary of the nickel silicide. Therefore the etchant agent penetrates into the nickel silicide and damages the nickel silicide. Hence, the electric performance of the nickel silicide is decreased.